The present invention relates to a sump unit used, for example, for fluid pressure circuit of anti-skid brake system for automobile.
In general, the anti-skid brake system for automobile is designed in such structure that the brake fluid in the wheel cylinder is released to a sump unit by switching over the electromagnetic valve when the skid condition of the wheel is detected during braking operation. Thus, by decreasing the brake pressure of the wheel cylinder, skid is eliminated. After the skid condition of the wheel is eliminated, the electromagnetic valve is switched over to increase the brake fluid pressure of the wheel cylinder in order to shorten the braking distance.
As the sump unit to be used for the fluid pressure circuit of the anti-skid brake system, the sump unit as shown in FIG. 2 has been conventionally used.
In FIG. 2, the sump unit 1' is mounted in such manner that it is communicated with the operating fluid passage 4, leading from the electromagnetic valve 2 to the oil pump 3. Namely, the sump unit 1' is installed on the main unit of the anti-skid brake modulator 5, and it is provided with a bore 6' having one end communicated with the operating fluid passage 4 and the other end opened outwardly and also with a piston 7' slidably engaged in this bore 6'. This piston 7' is pushed toward the operating fluid passage 4 at all times by a spring 8. The end of the spring 8 opposite to the piston 7' is supported by a spring receptacle 10 fixed on the main unit 5. On the side of the piston 7' facing the operating fluid passage 4, a fluid accommodating chamber 1'a is formed by the piston 7'.
In the sump unit 1' having such structure, when a wheel is in skid condition, the electromagnetic valve 2 corresponding to the wheel in skid condition is switched over, and the brake fluid discharged from the wheel cylinder of the wheel is sent into the fluid accommodating chamber 1'a.
Because the bore 6' is branched off from the operating fluid passage 4 in such sump unit 1', the sump unit 1' extensively protrudes from the operating fluid passage 4 to the lateral direction. For this reason, it is necessary to keep larger space for the sump unit 1', and this means the increase of the size of anti-skid brake modulator.
The fluid accommodating chamber 1'a of the sump unit 1' is formed just like a blind alley. Therefore, the air intermingled with the operating fluid in the fluid accommodating chamber 1'a cannot be efficiently withdrawn.